Switching a spin-valve back and forth by current-induced domain wall motion

We have studied the current-induced displacement of a domain wall (DW) in the permalloy (Py) layer of a Co/Cu/Py spin valve structure at zero and very small applied field. The displacement is in opposite direction for opposite dc currents, and the current density required to move DW is only of the order of 10^6 A/cm^2. For H = 3 Oe, a back and forth DW motion between two stable positions is observed. We also discuss the effect of an applied field on the DW motion.Comment: 4 pages, 3 figure

Magnetization reversal by injection and transfer of spin: experiments and theory

Reversing the magnetization of a ferromagnet by spin transfer from a current, rather than by applying a magnetic field, is the central idea of an extensive current research. After a review of our experiments of current-induced magnetization reversal in Co/Cu/Co trilayered pillars, we present the model we have worked out for the calculation of the current-induced torque and the interpretation of the experiments

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions

We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.4 nm (25 to 7500$ atoms) prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared to previous structural characterizations. The distribution of activation energies was independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant Keff. We find that Keff is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal is shown to proceed classically down to the lowest temperature investigated (1.8 K).Comment: 13 figures submitted to Phys. Rev.

Angular dependence of the tunnel magnetoresistance in transition-metal-based junctions

International audienceWe have investigated the angular behavior of the tunnel magnetoresistance ͑TMR͒ in transition-metal-based junctions using the low-field susceptibility of the crossed magnetic configuration. The noncollinear arrangement , stabilized by combining step anisotropy and interfacial exchange-bias coupling, is shown to be of a particular interest for an accurate analysis of the angular dependence of the TMR. We show that the intrinsic tunnel processes are reflected on a linear behavior of the conductivity giving a more complex form for the resistance, as expected by the model of Slonczewski. The more intuitive ''high-field'' saturating regime deviates the hard layer from its nominal pinning direction and consequently is shown to be less adapted for the experimental study of the intrinsic angular response of the TMR

Magnetic characterization of granular Co/Al2O3 multilayers

We study the magnetic properties of Co clusters with diameters between 0.8 and 3 nm prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data. Comparing this to the distribution of activation energies, obtained from the AC susceptibility, we have determined accurately the effective anisotropy constant Keff. We find that Keff is enhanced with respect to the bulk value and it increases as the average particle size decreases.This work has been partly funded by Spanish Grant MAT 99/1142 and the European network MASSDOTS.Peer reviewe

Electrical characterization of nanocontacts fabricated by nanoindentation and electrodeposition

We report on the electrical characterization of various types of nanocontacts fabricated by nanoindentation and electrodeposition. Arrays of holes with depths ranging from 0 to 20 nm were produced by nanoindenting at different strengths an Al2O3-50 Angstrom/NiFe-150 Angstrom//Si bilayer. NiFe was then electrodeposited, which led to the growth of particles in the holes. The resistance of the particles was measured with a conducting tip atomic force microscope. Depending on the strength used during the nanoindentation, the resistance ranges from less than 5x10(3) Omega to more than 10(12) Omega. The low-resistance constrictions can be used to study ballistic transport in materials. High-resistance contacts presumably correspond to tunnel nanojunctions. (C) 2002 American Institute of Physics